Introducing the Minus Sign

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Objective

Students will be able write a subtraction equation using the minus sign.

Big Idea

Students will learn the meaning of the minus sign. The minus sign is introduced using a fun song!

Problem of the Day

5 minutes

I start each math lesson with a Problem of the Day.  I use the procedures outlined here on Problem of the Day Procedures.

Today's Problem of the Day:

Laura had 10 balloons. Her brother popped 6 of them. How many balloons does Laura have left?

I set this problem up with some structure to help the students organize their thinking.  I give a blank line to remind students to write their answer.  I also include 10 balloons.  These balloons are interactive, so the students can actually pop 6 of them!  If you do not have a SMART Board, you can use the PDF and manipulatives, pictures or students drawings.

Since we do this whole group, I have one student come up and do this problem.  I remind the student to check their work when they are finished and have the class tell if they agree or disagree by showing a thumbs up or thumbs down.  


 

Presentation of Lesson

25 minutes

I start this by playing a song called The Minus Sign and talking about the minus sign.  Check out why I like it here.

I then give two students papers with numbers on them.  I have them stand in the front of the room.  I hand another students a paper with a minus sign and place that student in between the others. 

This is a minus sign.  It is the symbol that we use to show that we are subtracting.  We read this as 5 minus 3.  This is kind of like a sentence that we use in reading, but it is a sentence with numbers.  A number sentence is called an equation.  Just like a sentence in reading, the parts needs to be in the correct place for it to make sense. We need to keep the minus sign between the two numbers that we are subtracting.   We put the answer to the right.  In addition we call the answer the difference.

When we are finished, I tell students that they are going to be practicing using a minus sign on an Introducing the Minus Sign Worksheet.   I use the procedures outlined here on the Paper Procedures

Count the pictures. Write the numbers and minus sign to complete each equation.

The first thing the directions tell you to do is count the pictures and write the number to complete each equation.  You also need to write the minus sign.  For the first few questions, the minus sign is there and you just need to trace it.

We work through this paper together.  For these equations the equal sign is replaced with the word is.  When we read the equations we use the word is instead of equals.  I do this today to keep the students focused on the minus sign.  Many students get confused about which symbol is the minus sign and which is the equal sign, so I like to teach them on different days.  Even though we have already learned about the equal sign, I still want to keep that separate for now.  I walk around and make sure that students are correctly counting and writing their equations.  When students are finished with their paper, they can put it in the basket and get their center.

Practice

20 minutes

The centers for this week are:

 

I quickly circulate to make sure students are engaged and do not have any questions about how to complete the centers.  Because of the trouble during our addition unit, I decided not to introduce any subtraction centers this early in the subtraction unit. 

I pull 3 groups (5-10 minutes depending on need).  We are working on writing equations in all groups.  I verbally give the group an equation.  I have them write it and then solve it using manipulatives.  With students who are able to do this easily, I also have them try with drawing pictures instead of manipulatives. 

Prior to clean up, I check in with the other tables to see how the centers are going.  My students have been struggling with getting cleaned up quickly and quietly after centers.  Lately I have been using counting down from 20 slowly instead of a clean up song.  Counting backwards is as critical as counting up. Students need to be able to know the number that comes before, as well as after, any given number (w/i 10, w/i 20, etc.). Counting back is a critical strategy for subtraction.

The students like to count backwards with me as they clean up and I can lengthen or reduce the clean up time based on how students are doing and how much time we have.

Closing

5 minutes

To close, I put a student's paper on the document camera a project it on the SMART Board and have that student explain their work.  I have the class read the equation using the word minus.  I mention positive things noticed during centers as well as something that needs to be better next time. 

I review what we did during our whole group lesson.  "Today we learned about the symbol that is used in an equation to show we are subtracting.  Tomorrow we are going to learn about another important symbol that will make our equations complete!"